Combat PTSD Tied to Intensity of Fight

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Whether soldiers in combat develop post-traumatic stress disorder (PTSD) depends on their perception and attention to threat, the intensity of combat they are exposed to, and genetic susceptibility.

Note that a three-way interaction was observed between predeployment threat bias, combat exposure, and a polymorphism in the serotonin transporter gene.

Whether soldiers in combat develop post-traumatic stress disorder (PTSD) depends on their perception and attention to threat, the intensity of combat they are exposed to, and genetic susceptibility, a prospective study determined.

A significant interaction was seen between attention to threat and degree of combat exposure (β = −0.73, 95% CI −0.45 to −0.08, P<0.004), according to Yair Bar-Haim, PhD, of Tel Aviv University, and colleagues.

"Ample evidence indicates that attention is deployed in a biased, maladaptive pattern in PTSD and anxiety disorders, that such threat-related attention biases are plastic, shifting after exposures to danger, and that such biases predict PTSD symptoms in soldiers exposed to war-zone stress," they observed.

To examine soldiers' adaptability and attention to threat over time, Bar-Haim and colleagues conducted a longitudinal study from 2008 to 2010, which included 1,085 men whose mean age was 19 in the Israeli Defense Force infantry.

Participants underwent testing with a dot-probe task measuring response times to word targets on a screen that were either suggestive of threat or neutral.

"Threat bias" was calculated from the differences in reaction times when faced with a potential threat compared with a neutral stimulus. Positive bias scores represented faster responses to perceived threat, while negative bias scores reflected threat avoidance.

Symptoms of avoidance, hyperarousal, and intrusion were scored on the PTSD checklist, with a cutoff score of 50 being diagnostic. Assessments were made at the time of recruitment, 6 months later, after training and just before deployment, and after 6 months of deployment.

Combat exposure was classified as low or high, depending on factors such as proximity to actual combat zones and specific events such as being shot at or knowing someone seriously injured or killed.

Genetic analysis of the serotonin transporter gene 5-HTTLPR divided participants into low, intermediate, and high uptake of the neurotransmitter, which may influence their vigilance and ability to adapt to stress, according to the researchers.

The mean number of combat events was 2.03 overall.

The mean threat bias scores at baseline and before deployment for the 487 soldiers for whom all data were available were −1 and −3.

During deployment, the mean threat bias score was 21 in soldiers with high combat exposure, compared with 4 for those with low exposure.

At baseline, individuals who developed PTSD during deployment exhibited greater threat vigilance (P<0.001), while immediately before deployment, those who subsequently scored above the cutoff for PTSD showed greater avoidance of threat vigilance (P<0.05).

Two hypothesized interactions emerged as significant predictors of changes in threat vigilance: time x geo-operational exposure (P<0.006) and time x PTSD (P<0.01).

Other variables found to correlate with PTSD included high school education, baseline trauma history, and serotonin 5-HTTLPR allele frequency, and were included in a final model.

The full model predicted 34% of variance in symptoms of PTSD, an effect that was statistically significant (F=19.90, P<0.001), with these individual factors being predictive:

When these analyses were repeated for the entire cohort, the model explained 34% of variance in symptoms of PTSD in the high exposure group and 36% in the low exposure group.

These findings suggest that military deployment leads to alterations in threat bias, through interactions between level of exposure and 5-HTTLPR status.

"Specifically, soldiers with low-transcription 5-HTTLPR genotypes, particularly when they display threat vigilance in combat, a 'normative' response in the current sample, manifest fewer PTSD symptoms when exposed to combat stress," the researchers explained.

The findings suggest a possible means of treatment, through manipulating threat biases with a computerized training program used for anxiety, but further work will be needed to determine the suitability of such programs following combat exposure.

Limitations of the study included the inherent variability of data collected in circumstances of combat, and the lack of complete data for many participants.

The study was supported by the Leo and Julia Forchheimer Foundation in collaboration with the Mount Sinai School of Medicine, and by the National Institute of Mental Health.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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